Apparatus for producing low structure carbon black



J. C. KREJCI March 30, 1965 APPARATUS FOR PRODUCING LOW STRUCTURE CARBON BLACK Filed May 29, 1961 mv mN mm I.'

UntedStatesPatent Ot 3,175,888 APPARATUS FOR PRODUCING LQW vS'EWUCTURE CARBON BLACK Joseph C. Krejci, Borger, Tex., assigner to Phillips Petroleum Company, a corporation of Delaware Filed'May 29, 1961 Ser. No. 123,336 1 Claim. (Cl. 23h-259.5)

This invention relates to a process for making relatively low structure carbon black and to an apparatus for manuprocess foi-making relatively low structure carbon black by introducing `a vaporous hydrocarbon Aaxially intro a zone wherein a helical flow of hot gases is maintained Yby introducing these gases tangentially and wherein these gases coin-prise combustion products containing appreciable amounts of excess fuel. In `another aspect this invention relates to apparatus for the manufacturingV of relatively low `structure carbon lblack comprising means for injecting `a vaporcus hydrocarbon axially into a chamber `and means for introducing hot gases tangentially into the chamber including Aa combustion chamber, conduit means for conducting the combustion products to the tangential inlet andy-means for introducing additional unburned fuel into the conduitrneans. t Y

By structure of ia` carbon black is meant characteristics which relate to occulation of the carbon black particles.` The structure issaid to be high When-there is a strong tendency for the particles to: form chains `of particles. Conversely the, structure is said to be low when there is little tendency to lform such chains.

High structure carbon blaclcis generally considered to be one having an oil absorption of about 1.35 to 1.45 and this is the usual range for :furnace blacks. Normal structure is considered to be about 0.75 to 1.2 and has generally been made bythe channel black process. Low structure is considered to be about 0.45 to 0.55 and is made by the thermalprocess' Recently, however, furnace blacks having relatively low structure for blacks ci this type have been marketed. These blocks have, in some instances, proved tto be useful in applications formerly served by channel blacks, forexarnple, in reinforcing natural rubber products and in `specific applications, for example, .in non-squeal soft-riding tires. These blacks often are designated low structure blacks because they are lower .than normal for blacks made by bhe: iur-nace process even though their oil absorption values Itall in the upper portion or the range of lthe blacks generally desig-` unpelleted black. Working tendsto reduce this value and `pelleted `blacks have values approximately 0.1 lower in all ranges.

i facturing such carbon black. In lone aspect it relates to i ice a tangential rotating stream of hot gases in a carbon black furnace. y

Another objectof my invention is to provide apparatus for producing relatively low structure furnace carbon black. t Other aspects, objects and advantages of invention are vapparent in the Written description, the drawing and the claim.

According to my invention there is provided a process for producing relatively low structure carbon black which comprises establishing a rotating mass` of hot gases comprising combustion products containing at least about 20 percent of excess fuel in a generally cylindrical rst zone having a diameter greater than its length andl maintaining a temperature in the rotating mass above approximately 2400" to 2600 F. by` continuously injecting additional hotgases, continuously passing a portion of the rotating gases into` a generally cylindrical second zone having a length greater than its diameter and -a diameter less than that of the tirst zone, incommunication with and in axial alignment with the first zone, feeding a vaporous or atomized hydrocarbon along the axis of the first zone and passing it axially through the rotating mass of the first Zone g and axially into the center of the rotating mass in the second zone, forming `car-bon black from/the vaporous hydrocarbon bypyrochemical action due to the heat of the surrounding hot gases and separating the carbonvblack from the resultantgaseous products ofthe process. The

lhot gases can be -supplied Vby burning a normally gaseous amount of the free oxygen-containing gas. The fuel 'gas` can be a residue natural gas and the free oxygen-containing gas can be air, in which case the stoichiometricratio of air to gas is about l0 and the preferred ratio is `between about 6 andV-about 8.

Also accordingto my invention the hot` gases can be produced by burning a fuel with sufficient free-oxygen containing gas to produce a readily combustible mixture and injecting additional fuel into the resulting combustion products to produce a mixture containing at least about 20 percent of excess fuel. This procedure is particularly useful when the fuel is normally liquid and difficulty is found in `maintaining combustion at the rich mixture desired. Y

Further `according to my invention there is provided` apparatus for .producing relatively low structure carbon black which comprises a first generally cylindrical chamber having a diameter greater `than itsV length, a secondchamber having `a'length greater than its diameter land` a diameter` less than :that of the first chamber, in communicationwith and in axial alignment with` the first chamber, meansffor introducing hot gases tangentially into the first chamber comprising a combustion chamber, means for,l injecting a fuel and a free oxygen-containing gas into the combustion chamber, conduit means lfor conducting the hot gases from the combustion chamber tothe first chamber and means in communication with the conducting means for injecting additional unburned fuel.` l

FIGURE 1 is a longitudinal sectional view of a furnace embodying my invention, taken on the line 1--1 of FIG- URE 2.

FIGURE 2 is a transverse sectional view of the same furnace taken on the line 2--2 of FIGURE 1.

FIGURE 3 is a transverse sectional view of a modified furnace having an enlarged portion downstream of the second chamber.

The drawing is diagrammatic and such parts of the apparatus as feed lines, air carrying pipes, combustible gas pipes, pumps, valves, meters, pressure regulators, pressure measuring devices, temperature measuring devices, and other conventional apparatus are shown schematically or have been eliminated from the drawing to avoid unnecessary complication.

In ythe apparatus illustra-ted in FIGURES 1 and 2, a

' first short cylindrical chamber 10 having a rather large diameter is axially aligned with smaller diameter relatively long chamber 11 and chambers 1@ and 11 have a lining 12 of highly refractory material such as sillimanite, alumina or other. refractory suitable for the temperatures and materials encountered. Between the refractory liner 12 and the cylindrical steel shell 13 is a layer of insulation 14. In the upstream or inlet end wall of chamber 10 is a feed pipe 15 arranged axially so that feed introduced therethrough passes axially through the furnace. Sur- 1 rounding feed pipe 15 is a larger pipe 16 thus defining an annular space 17 through which air or other gas lcan pass into the furnace. The purpose of the gas passing through space 17 is to keep the inner end of feed tube 15 cooled to prevent the deposition of carbon thereon.

Around chamber 10 there are arranged inlets 20 which are disposed so that gas passing therethrough into chamber 10 does so in a direction tangent to the cylindrical wall. Each tangential inlet 20 comprises a combustion chamber 21 and a conduit 22 which latter terminates as an opening in the refractory liner 12 of chamber 10. A pipeZS extends part way into combustion chamber 21 as shown. Separate conduits 24 and 25 are provided for feeding fuel and an oxygen containing gas, respectively to pipe 23. An inlet 26 is provided for additional fuel which can 4be supplied through pipe 27.

At the outlet end of the furnace is a cooler assembly 30 and a carbon black separating or recovery means 4u. Cooler assembly 30 includes a' water jacket 31 having inlet and outlet pipes 32 and 33, respectively, a spray nozzle 34 and a water supply pipe 35 therefore. A conduit 36 connects cooler assembly 30 with carbon blackv separating means 40. Off gas is taken from means 4t) through pipe 41 while carbon black is removed through pipe 42.

In operation, a suitable fuel is fed through the pipes 25, mixes with a free-oxygen containing gas supplied through pipes 24 and a combustible mixture fed through the pipes 23 into combustion chambers Z1 where combustion takes place. The hot products of combustion then flow through the conduits 22 and enter chamber 11B tangentially. Although 2,1 is designated as combustion chamber, in many instances a substantial amount of cornbustion also takes place in conduit Z2 and some may occur in chamber ltl, but the combustion is complete prior to mixing of the hot gases with the axial feed. The reactant enters through pipe 15 axially into chamber 1t? and thence axially into chamber 11. Heat is transferred from the rotating hot gases to the axially fed reactant,

lthus converting or decomposing the reactant hydrocarbon to carbon black, the heat being transferred by mixing at the interface between the hydrocarbon and the cornbustion gases or by radiation, or both. Upon issuing 'K from the reactor the gaseous efliuent carrying the carbon a, nasse low structure.

. 4j precipitator or cyclone separators, etc. When the hot gases entering chamber 10 contain between about 20 percent and about 40 percent of excess fuel and no substantial amount of air is added to the reaction zone, the resultant carbon black product has relatively low structure.

The furnace illustrated in FIGURE 3 is similar to that illustrated in FIGURE 1, corresponding parts being chambers 1G and 59, chambers 11 and 51, pipes 23 and 43, 15 and 45, 16 and 46, 24 and 48, 25 and 49, and annular spaces 17 and 47. o

As pointed out above, by structure as herein applied, is meant the surface characteristics of the carbon black particles whereby these particles have a strong tendency to link together to form chains of particles. Where the tendency is strong to form particle chains, the black is said to have hiUh structure, Whereas when there is little tendency to form such chains the black is said to have Since 'it is not convenient to measure the structure directly, the oil absorption of the black, which has been found to correlate closely, often is used as a measure of the structure.

Oil absorption is measured by adding oil a few drops at a time to a one gram sample of carbon black on a mixing stone or glass plate. After each addition Ythe oil is incorporated thoroughly with a spatula, using moderate pressure. Tiny pellets are formed, gradually increasing in size as more oil is added. The end point, approached one drop of oil at a time, is reached when a single ball of stiff paste is formed. The results are reported as cc. oil per gram of black or converted to gallons of oil per pounds of black. n

Although oil absorption correlates closely with struc-v ture, it is also affected by particle size. Particle size is a function of the total volumetric throughput which is determined to a large extent by the amount of tangential gas supplied. Further, in the production of carbon black, the temperature and the time of treatment are controlled to obtain a maximum of conversion with a minimum of after-treating. Since the time of treatment is determined by consideration of particle size, the conversion is controlled by temperature. This is regulated by regulating the amount of reactant introduced, too large an amount resulting in lower than desired conversion while too small an amount results in'aftertreatment. By my` invention, relatively low structure carbon black is produced by using aV lower than normal air fuel ratio at any desired throughput and temperature.

In this application, the incoming hot gas stream is characterized in two ways, (l) by percent ytheoretical air, the ratio of oxygen supplied to the theoretical (stichiometric) amount required for complete combustion of the tangential fuel, and (2) by percent excess fuel, the ratio of excess fuel to the actual fuel. The first is calculated as follows:

while the second isV calculated Yas follows:

Actual fuel (lbs./hr.) -theoretieal fuel (lbsL/hr.)

Actual fuel X 100 These values are related in the following manner:

Percent theoretical air-l-percent excess fuel=100.

VThus, by calculating as suggested, these values are easily compared. Where all of the fuel enters with the oxygen-containing gas, it is convenient Yto characterizeA the hot gases entering the reactor as produced'by burning the fuel with a specified percentage ofthe stoichiometric;

the percent of excess fuel is in the range of about 20 to about 40 percent, corresponding with about 80 to about 60 percent of theoretical air.

The amount of gas which enters through annular space 17 can be varied widely, but always is relatively small as comparedwith theu tangential gas. This annular gas `is not esesntialrto the practice of my invention and can be dispensed with entirely, However, I prefer to utilize a' small amount of gas tokeep theinner end of feed pipe cool to prevent carbon deposition thereon. The

`amountof gas supplied in this manner is not a large percentage of the total gases present in the reactor. If the gas is air it is not substantial as compared with the total l air supplied to the tangential fuel and, in any case, is

not enough to cause the percent of excess fuel present in the hot gases which contact the axial oil feed to be outside the specified range of about to about 40 percent.

YIt is essential that the hot gases which contact the oil `feed be maintained in the fuel rich condition. These fuel rich that the combined gases are within the range of about 20 to about 40 percent excess fuel.

l Suitablem-aterials-for use as the feed for conversion to carbon black include oils, such as kerosene, gasoline boiling range hydrocarbons, heavy or light naphthas or oils. Such hydrocarbon materials as natural gas, either dry gas, we t or raw natural gas as it comes from a gas well, or gasoline extraction plant or refinery residuergas may be used. Further, heavier, hydrocarbons than natural gases may be used as charge, such as butane, pentane, or the like. Thus, Vmost hydrocarbons can be used as feed in my furnace.` The feed may be injected as a liquid through a spray or atornizer, although llprefer to operate with the -feed injected as a vapor. Hydrocarbons from other sources than petroleum likewise are suitable, as for example, low temperature coal gas, coal tar distillates, shale gases and distillates may be used. These charge stocks `may `contain almost any class of hydrocarbon compound, as for example, saturatedor unsaturated hydrocarbons, parains, ole-fins, aromatics, naphthenes, or any others which might become available. An aromatic `gas, oil such as .described is, however, a preferred feed stock. t

As is Well known, the carbon blackV yield is higher with high aromaticity (high BMCI). Therefore, al-

Y "though lower structure blacks can be obtained with lower Varomaticity feeds, this is generally uneconomical because of the corresponding low yield. By the practice of my invention, a lower structure iSobtainable with a `given ."feed. Therefore, it is possible to obtain a lower structure for a given yield, or a higher yield for a given structure. Thereforerit does not relate `to a specific value or range of values of structure since this is determined to `some extent bythe feed chosen. However, forthe commonly used-furnace'black feedstocks whichare, as noted above, aromatic gas` oils and have a BMC-l between about Helium 0145 Methane 78.71 Nitrogen 9.0i Propane 3.',45 Ethane 7.82 vt-nutane 0,15 CO2 A0.32 nButane `0.09

Total 100.00

Residue natural gas is a preferred tangenital fuel. typical residue gas has theV following analysis:

HoWevenfother fuels may be used. For example, hydrocarbon oils as a spray or vapor, or gases other than natural gas (predominately methane) or mixtures of oil and gas or even powdered `solid fuels may be used but fluids arepreferred. Water gas, producer gas, coal gas, or even hydrogen can be used but are not preferred. One skilled in the art can readily determine or calculate the amount of air or other oxygen-containing gas necessary forthe combustion of a particular fuel when the composition is known. Once the theoretical air-gas ratio 1 s determined, the operating limits for the practice of my invention can be determined readily using the limits of about 60 to about 80 `percent of this'theoretical (stoichi ometric) ratio.

When a gas con- The following examples illustrate the operation of my invention.

EXAMPLE I An axial feed having the following `properties was used:

`ASTM distillati@ [Gorrected to 760 mm.]

10% F 481 20% 492.` 30% F` 503 40% F-.. 514 %V F 524` `F 540 F-- `560 F 595 F-; 654 End point F 703 Recovery 97.5 Pour point -30 Carbon residue, Conradson, wt. percent 0.16 Gravity, API 20.8 Aniline No. 57.() BMCI 72.3 Flash, Pensky-Mantins, Ff 185 Color, NPA i Dark Molecular wt. (mean ave.) 202 Carbon content, wt. percent (est.) 88.0

o The oil feed described above was preheated to 700 Y 1 F. prior to being introduced into pipe 4S. Residue natural gas was used as the fuel gas feed through pipes 49 while` Van' was `fed through pipes 4u to `mixttherewith, the mixtureentering pipe 43. The pipe de terminated adjacent the wall of chamber 10. Conditions and results of these runs are shown in Table I, Runs No. P-137, P449, P-

l5() and P-152. Inrthese runs, the reactor, asillustrated i 1n FIGURE 3, chamber 50 had a diameter of33 inches and a length of l2 inches whilerchamber 51had a 69 inch length with a l2 inch diameter adjacent chamber 50 and a 63 inch length having a diameter of 2l inchesin lower air/fuel ratio,` hada lower structure.

These runs were made in a reactor as illustrated in FIGURE 1 in which the chamber 10 was 37 inches in diameter and l2 inches long, chamber 11 was 12 inches in diameter and 11 feet long, and there was a section 18 inches in diameter and 12 inches long downstream of chamber 11. Ay mixture of residue natural gas and air was used a the tangential' fuel. Conditions and results are illustrated in Runs No. P-979R-J1, P-980, P-981, P982, P-984R- 1, P-985 and P-986 in Table I. Here again, the reduction in structure with reduction in air/fuel ratio is demonstrated. 'f

in Example I, illustrating that higher structure is obtained TABLE I Run Oil rate, Preheat Tangentiai Tangentiai Air to gas Axial gas, Photelo- Nitrogen CHCla Tinting i Oil l Number gal. mp., F. air, fuel gas, ratio meth. meter surface Color strength, absorption v lm.c.i.h. n1.e.f.h. area Y percent Y 45 700 25 1.` 67 15 Clear 121 1.13 85 700 60 3.33 15 1.16

- -70 700 100 13.33 7.5 0. 98 185 700 125 8. 33 15 1. 27 154. 2 755 148 9. 86 15 157. 5 1. 35 250. 3 755 14s Y 0. 86 15 75. 2 1. 35 04. 775 140 18. 67 7. 5 83. 4 1 1. 17 05. 5 775 140 18. 67 7. 5 89. 4 1. 14 49.4 775 140 18.67 7.5 09.5 1.12 41.3 775 140 21. 54 g 6.5 106.3 1.05 221.4 775 140 0.33 15 78.0 1.37 170.3 775 140 0, 33 15 80.3 1.30 80. 6 775 125 12. 5 10 Fuer gas-3- Y 90 07. 8 1. 27

EXAMPLE II 25 at these higher air-fuel ratios. The oil had the following S 1 d f d l h characteristics: j

evera runs were ma e wit a ee o1 comprising an v l. SO2 extract having the following characteristics: ASTM dstllatr'o" ASTM distillation 30 [Corrected t 760 1m-1 IBP F-- 428 [Corrected to 760 mm.] 5% p 471 FD F 470 10% F 482 5% F 558 20% F-- 493 10% P 586 35 30% F-- 502 F 611 40% F 513 F 639 50% 13 7` 524 F 660 60% p 538 F 681 70% p 552 --V--y F 711 40 80% p 590 F 761 90% F 643 --f-,. F 820 E13, F 685 82%, F 867 Percent recovery .percent 98.0 Pour pomt F 45 y Pour point F-- 25 Carbn residue, wt. percent --Y 1-61 Carbon residue, Conradson 0.18 Gravur. API 11-0 Gravity API-- 19.0 Refractive index, 20/D 1.5854 Angine NO p 50 7 BMCI 90-4 BMC1 776 Viscosity, SUS, F. g1-9 50 Flash (p1/1 p 200 Viscosity, SUS, 210 F. 37-6 C0101 (NRA) Dark Carbon, wt. percent 88.8 l Hydrogen, Wt- Percent These runs were madein a furnace and with the same Sulfur Wt percent 0'17 r tangential'components as described in Example II. Con- BS & W1. V01- Plefnt r.- 0'44 5 ditions and results are given in Table I, Runs No. V1)-70, Penta msolb. e Wt- Percent i P-72 and P-74. These runs illustrate that, with a feed having an aromaticity in the same range as that of Example I, higher structure is obtained with an air/fuel ratio 'of 15.

samples from Runs 13-97911-1, yP-980, P-981, P-982,

P-984R-ljP-985 and P-986 Were compounded with natural and synthetic rubber and vulcanized. The compounding recipe for synthetic rubber was: f

`eral different times,"20, 30, 45 and 75 minutes. After vulcanization for 30 'ninutes the compound possessed properties as given in Table II, except for the 300 percent `modulus average `which was obtained` fromihe average of all cures. After oven aging for 24 hours at 212 F.

the compounds possessed the` properties given in Table 110 i The compounding recipe for natural rubber was:

I Parts by weight #1 Smoked Sheet 100 Carbon black 40 Stearic acid 3 Zinc oxide 5 Altax 5 0.6 Sulfur 2.5

Airex 5 is benzthiazyl disulfide (cmNCs-Zs.. These compounds were vulcanized 51293` for various III. times as shown in Table 1V.

TABLE Ii Compres- `Crossi Run Number sion Set, linking, 300%-Modulus ATF Permanent VResilience.,

Percent X104 Tensile, Elongation, "Set, Percent Percent mois/cc l p.s.i. Percent Avg. A11 30 Min., Cu.res,l p.s.i. p.s.i.

Research Compounding Section Controls` Abrasion Com- Extrusion at 250 F. Tear Strength Shore pounded, Hardness MS 1% i Loss, g. Index f iin/mln. gJmin. 80 F.,1b.,in. 200 F., lb./in.

Research Compounding Section Controls *20, 30, 45 and 75 minutes.

TABLE III 80 Abrasion Run Number 300%-Modulus v AT5` `Permanent Resilience, y

p Eiongation, Set, percent percent Tensile, p.s.i. percent Loss, g. Index Avg. All 30 Min., Cures,* p.s.i. p.s.i.

1, 030 1, 700 3,200 400 60.5 "0s 00.9 8.02` 121 1, 750 1, 850 3,065 420 54. 4 0.6 66; 4 9. 75 110 `1, 790, 1,865 3, 170 430 55. 1 0.` 7 65. 3` 9.15 118 1, 700 1,800 3,325 440 57. 8 0.7 64. 6 8. 91' `121 1, 840 2, 010 3,170 410. 57. 5 A0. 7 64.1` 8. 50` i 126 2, 2, 225 2, 850 370 59. 5 0. 7 64. 2 8. 53 126. 2, 2, 300 2, 990 370 58. 8 0. 8 64.7 8.62 1,25 1, 725 1, 825 2, 650 400 57. 1 0. 8 65. 2 `10. 76 100 1, 990 2, 3,060 380 61.9 0. 7 62. 1 7. 91 136 1, 540 1, 660 2, 810 420 55.8 0. 9 64,'3 11. 13 97 20, 30, 45550 `75 minimes.

TABLE IV 13155k P-982 P979R1 P980 P-981 P-085 P-985 P-984R-1 IRB #1 PBI #3 Rcg51300 compounded MLA at 21211 57.8 58.0 70.0 70.0 72.0 72.0 72.5 57.3 74.0 55.0

Physical Properties (Cured at 293 F.)

1.07 1.19 1.13 1.13 1.10 1.21 1.18 .94 .95 .97 1. 52 1. 71 1.55 1. 54 1. 55 1. 82 1. s3 1. 54 1. 45 1. 47 1.80 1. 92 1. s0 1. 89 1. 85 1. 95 1. 95 1.77 1. 82 1. 75 y 1.89 2.00 1. 92 1. 05 2.00 2.15 2.18 1.95 1.89 1.84

TheV following tests were used to obtain the data of ASTM distillation-Continued rabies 111115115 1v: 35 Gravity, API 10.5 A Compression Set-ASTM D395-55 Method B, modl- Aniline No, p 82A fied (0.325 inch spacers), compressed two hours at 212 BMCI 935 F. plus relaxation for one hour at 212 F. Viscosity;

Cross-linking-determined from reciprocal Volume 100 F SUS 8424 `swel1 and equilibrium modulus as described in Rubber 40 210 F "SUS" 36 12 World, 135, 67, 254V (1956)- Carbon wt. percent-- 89.0 Modulus, tensile and elongation, ASTM D412-51T. Hydrogen don 9 6 ATF and Permanent Set, ASTM D623-58 Method A. Sulfur d0 1 3`7 Resilience-Lupke Rebound, Vanderbllt Rubber BS & W v01 pere'nt 0 09 Handbook, 2220 (1958)- Refractive Index, 20/D l 1.5874

Shore hardness-ASTM D676-58T.

Abrasion loss--modied Goodyear Huber Angle Abradh(er, 24 inch wheel, 11/2 inches thick, Grade M, vitreous, grain size No. 36, Alundum of the Norton Company, Worcester, Massachussets.

Compounded Mooney-ASTM D927-57T, Mooney viscometer, small rotor, 1.5 minutes, 212 F.Y temperature. Extrusions--No. 1/2 Royle extruder with Garvey die, as described in Ind. Eng. Chem., 34, 1309 (1942).

Tear strength-ASTM D624-54, razor-nicked crescent specimen.

EXAMPLE IV Two runs were made with a fuel oil having the following characteristics:

ASTM distillation ,'[Corrected to 760 mm.]

These runs were made in a reactor as illustrated in FIG- URE 3 in which chamber 50 had a diameter of 37 inches and a length of 12 inches while chamber 51 had a diameter of 12 inches for a length of 132 inches followedl by a diameter of 15 inches for a length of 46 inches. These runs, which are P4818 and P-830 in Table I, show that oil feed rate alone does not determine structure;

Throughout this application BMCI refers to a correlation index developed by the Bureau of Mines and is used to denote aromaticity of an oil; a higher numerical index denotes a more armomatic oil.

lated yfrom the formula Y C.1.=18-49+473.7G-455.8 where:

C.I.=Bureau of Mines correlation indexV K=average boiling point K.) of the fraction G--specific gravity 60 F./60 F. of the fraction Reasonable Variation and modication are possible within the scope of my invention which sets forth method The indexis calcu-V ucts to said first chamber downstream of said means for introducing a fuel and a free oxygen-containing gas into said combustion chamber.

References Cited in the le of this patent UNITED STATES PATENTS 2,564,700 Krejci Aug. 2l, 1951 2,782,101 Heller Feb. 19, 1957 2,852,345 Rushford Sept, 16, 1958 2,918,353 Heller Dec. 22, 1959 2,985,511 Norris et al May V23, 1961 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,175,888 March 30, 1965 JosephCe Krejci l It is hereby certified that error appears in the above numb-ered patent requiring correction and that the said Letters Patent should read as Corrected below.

Column 13, line l, after "said", second occurrence, lnsert second Signed and sealed this 17th day of August 1965.j

(SEAL) Attest:

ERNEST W. SWDER EDWARD J. BRENNER Anesting Offir Commissioner of Patents 

